Re: [PATCH 05/17] freezer: rename thaw_process() to __thaw_task() and simplify the implementation

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 11/01/2011 12:35 AM, Tejun Heo wrote:
> thaw_process() now has only internal users - system and cgroup
> freezers.  Remove the unnecessary return value, rename, unexport and
> collapse __thaw_process() into it.  This will help further updates to
> the freezer code.
> 
> -v2: minor style update as suggested by Matt.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Paul Menage <menage@google.com>
> Cc: Matt Helsley <matthltc@us.ibm.com>
> ---
>  include/linux/freezer.h |    3 +--
>  kernel/cgroup_freezer.c |    7 +++----
>  kernel/freezer.c        |   31 ++++++++++++-------------------
>  kernel/power/process.c  |    2 +-
>  4 files changed, 17 insertions(+), 26 deletions(-)
> 
> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
> index 4a73dd2..253bcfe 100644
> --- a/include/linux/freezer.h
> +++ b/include/linux/freezer.h
> @@ -45,7 +45,7 @@ static inline bool should_send_signal(struct task_struct *p)
>  }
> 
>  /* Takes and releases task alloc lock using task_lock() */
> -extern int thaw_process(struct task_struct *p);
> +extern void __thaw_task(struct task_struct *t);
> 
>  extern bool __refrigerator(bool check_kthr_stop);
>  extern int freeze_processes(void);
> @@ -183,7 +183,6 @@ static inline int frozen(struct task_struct *p) { return 0; }
>  static inline int freezing(struct task_struct *p) { return 0; }
>  static inline void set_freeze_flag(struct task_struct *p) {}
>  static inline void clear_freeze_flag(struct task_struct *p) {}
> -static inline int thaw_process(struct task_struct *p) { return 1; }
> 
>  static inline bool __refrigerator(bool check_kthr_stop) { return false; }
>  static inline int freeze_processes(void) { return -ENOSYS; }
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index e691818..e7fa0ec 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -130,7 +130,7 @@ struct cgroup_subsys freezer_subsys;
>   *   write_lock css_set_lock (cgroup iterator start)
>   *    task->alloc_lock
>   *   read_lock css_set_lock (cgroup iterator start)
> - *    task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
> + *    task->alloc_lock (inside __thaw_task(), prevents race with refrigerator())
                                                                   ^^^^^^^^^
                                              Shouldn't this be __refrigerator()?

>   *     sighand->siglock
>   */
>  static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
> @@ -300,9 +300,8 @@ static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
>  	struct task_struct *task;
> 
>  	cgroup_iter_start(cgroup, &it);
> -	while ((task = cgroup_iter_next(cgroup, &it))) {
> -		thaw_process(task);
> -	}
> +	while ((task = cgroup_iter_next(cgroup, &it)))
> +		__thaw_task(task);
>  	cgroup_iter_end(cgroup, &it);
> 
>  	freezer->state = CGROUP_THAWED;
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index 57ba75f..8faa0e0 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -145,18 +145,8 @@ void cancel_freezing(struct task_struct *p)
>  	}
>  }
> 
> -static int __thaw_process(struct task_struct *p)
> -{
> -	if (frozen(p)) {
> -		p->flags &= ~PF_FROZEN;
> -		return 1;
> -	}
> -	clear_freeze_flag(p);
> -	return 0;
> -}
> -
>  /*
> - * Wake up a frozen process
> + * Wake up a frozen task
>   *
>   * task_lock() is needed to prevent the race with refrigerator() which may
                                                     ^^^^^^
                                                __refrigerator()?

>   * occur if the freezing of tasks fails.  Namely, without the lock, if the
> @@ -164,15 +154,18 @@ static int __thaw_process(struct task_struct *p)
>   * refrigerator() could call frozen_process(), in which case the task would be
>   * frozen and no one would thaw it.
>   */
> -int thaw_process(struct task_struct *p)
> +void __thaw_task(struct task_struct *p)
>  {
> +	bool was_frozen;
> +
>  	task_lock(p);
> -	if (__thaw_process(p) == 1) {
> -		task_unlock(p);
> -		wake_up_process(p);
> -		return 1;
> -	}
> +	was_frozen = frozen(p);
> +	if (was_frozen)
> +		p->flags &= ~PF_FROZEN;
> +	else
> +		clear_freeze_flag(p);
>  	task_unlock(p);
> -	return 0;
> +
> +	if (was_frozen)
> +		wake_up_process(p);
>  }
> -EXPORT_SYMBOL(thaw_process);
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index addbbe5..fe27872 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -186,7 +186,7 @@ static void thaw_tasks(bool nosig_only)
>  		if (cgroup_freezing_or_frozen(p))
>  			continue;
> 
> -		thaw_process(p);
> +		__thaw_task(p);
>  	} while_each_thread(g, p);
>  	read_unlock(&tasklist_lock);
>  }

Rebasing to latest kernel, we need to do the conversion in mm/oom_kill.c as well,
(and consequently add __thaw_task() empty function under !CONFIG_FREEZER, in
include/linux/freezer.h)

Thanks,
Srivatsa S. Bhat